1. Field of the Invention
The present invention relates generally to electrical switching apparatus and, more particularly, to circuit breakers including a heat sink. The invention also relates to a heat sink for dissipating heat from an electrical switching apparatus, such as a circuit breaker.
2. Background Information
In operation, electrical switching apparatus (e.g., without limitation, circuit switching devices and circuit interrupters such as circuit breakers, contactors, motor starters, motor controllers and other load controllers) used in power distribution systems often generate significant heat. When such heat becomes excessive, undesirable side effects can occur, such as, for example, damage to electrical equipment. In an attempt to avoid this and other disadvantageous consequences, industry guidelines have been developed to define acceptable thermal profiles and temperature ranges at various locations on a particular electrical switching apparatus.
Low voltage power circuit breakers, for example, are subject to such thermal profiles. Generally, low voltage power circuit breakers, such as integrally fused, low-voltage power air circuit breakers, are designed for use in low voltage applications ranging in nominal voltage up to 600 VAC. Such circuit breakers can be relatively large and, therefore, are typically configured in a draw-out arrangement in which the circuit breaker is mounted on a movable frame or cassette that can be drawn out of a housing assembly in order to, for example, gain access to the electrical terminals and bus work on the back side of the circuit breaker.
Some low voltage power circuit breakers include integrally mounted current limiters. In general, a current limiter is connected in series to a standard frame low-voltage power circuit breaker in order to safely extend the maximum interrupting rating of the coordinated, series combination to a much higher value than would otherwise be available on the standard frame. Such current limiters are typically series connected to the line terminals of the low-voltage power air circuit breakers. When the low-voltage power air circuit breaker is used in conjunction with such limiters at relatively high continuous currents (e.g., without limitation, up to 5000 amperes), a thermal dam is frequently created at the line side terminals of the breaker by, for example, the current limiters, electrical bus work, and the various electrical connections at the terminals. The thermal dam can generate excessive heat which has a tendency to reflect back into the circuit breaker and can cause damage to the circuit breaker and associated electrical equipment. Additionally, industry regulations explicitly require the temperature at the location of the line bussing coming out of the low-voltage, power air circuit breaker to be below a certain temperature threshold. The aforementioned thermal dam can result in the circuit breaker failing to meet the industry maximum temperature rise requirement for this location, thus rendering the circuit breaker unsuitable for commercial applications. Accordingly, it is desirable to eliminate thermal dams or, at a minimum, to reduce temperatures of locations known to form a thermal dam.
There is a need, therefore, to expel heat from thermal dams present in circuit breakers.
There is, therefore, room for improvement in electrical switching apparatus such as circuit breakers.